Add rust_test and update TEST_MAPPING am: efbe0ef315 am: bbeeae3c36 am: c266fd138a

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/futures-sink/+/1366005

Change-Id: Iac5677de71f634194e3409739359e6e56eed4d16